Physical Description of Adult Butterfly:
Above, the male is dark brown with lower halves of both wings
in shining blue. In the forewing, there is a short and oblique blue band in the apical area, and a black oval band in the outer part of the cell. The female is mainly brown. In its hindwing, the tornal area is white with embedded black spots in space 1b, space 2 and in the tornal lobe. Underneath,
both sexes are mainly yellowish orange with the lower half of the hindwing white. Black post-discal striae are present in the tornal half of the hindwing. In the forewing, the basal part of vein 12 is black (this is a key characteristic for distinguishing the Great Imperial from the Grand Imperial). There are tails at the end of veins 1b and 2 in the hindwing. For the tail at end of vein 2, the one for the male is little more than a tooth, while that of the female is moderately long. As for the tail at end of vein 1b, the one for the male is long and sword-like, while that for the female is even longer and fluffy in appearance.

A newly eclosed male Great Imperial resting on its pupal case.

A male Great Imperial taking nectar from Syzygium flowers.

Field
Observations of Butterfly Behaviour: This species is rare in Singapore. The handful of sightings take place mainly in the Central Catchment Reserve, as well as small pockets of wooded area to its west and north. The Great Imperial appears to be a tree-top dweller. The fast flying adults typically perch with its wings closed upright between flights. In sunny weather, however, they have been observed to sun-bathe with wings fully open.

A female Great Imperial.

Early Stages:So far, two parasitic plants have been recorded as the host plant for the Great Imperial. The caterpillar feeds on the young leaves of both host plants, with the early instars mainly skimming the leaf surface while those in the later instars devouring the leaf lamina whole from the edge.

Local host plant #1: Scurrula ferruginea.

Local host plant #2: Dendropthoe pentandra.

The eggs are laid singly on the underside of a leaf of the host plant.
Each egg is about 1-1.1mm in diameter, creamy yellow in color when freshly laid. The surface is covered with conical protrusions with blunted tip. The tiny and depressed micropylar sits at the pole.

Two views of an egg of the Great Imperial.

It takes about 3 days for the egg to hatch, with the young caterpillar nibbling away the upper portion of the egg shell to emerge. The newly hatched has a length of
about 1.9mm. Its body has a white and pale yellowish ground colour with two sets of reddish patches on the sides. The pro-thoracic shield and anal plate are mainly brown in colour.
Each of the segments from the 3rd thoracic segment to the 7th abdominal segment has a dorsal conical protrusion. Pale brown setae emanate from these protrusions. The body also features rather long whitish setae along the body rim, and a rectangle-shaped posterior end. After hatching, the infant caterpillar proceeds to devour the remnant of the egg shell.

A newly hatched
caterpillar devouring the remnant of its egg shell.

Two views of a newly hatched caterpillar of the Great Imperial.

As the caterpillar grows
the reddish patches on its body expand their reach and become darker and more intense red at the same time. After about 4
days of growth in the first instar, and reaching a length of about
3.3mm, the caterpillar moults to the next instar.

Two views of a 1st instar caterpillar, late in this stage, length: 3mm.

Two views of a 1st instar caterpillar, dormant before its moult.

The 2nd instar caterpillar has much shorter (proportionately) dorsal and lateral setae. It prothoracic shield is dark brown to black in colour. The previously rectangular posterior segment now has two small conical protrusions. The dorsal nectary organ on the 7th abdominal segment is now discernible. The 2nd instar caterpillar grows steadily and reaches a length of about 6-6.5mm. After about 4 days in this instar, it moults again.

Two views of a 2nd instar caterpillar, early in this stage, length: 3.6mm..

Two views of a 2nd instar caterpillar, later in this stage, length: 5.2mm..

Two views of a 2nd instar caterpillar, late in this stage, dormant prior to its moult.

The 3rd instar caterpillar resembles the 2nd instar caterpillar, but with various features (such as dorsal and posterior conical protrusions, body outline) becoming more pointed or angular. Numerous setae covering the body are now proportionately shorter and uniform in length. The dorsal nectary organ is also rather large and more prominently featured than in the 2nd instar. The pair of tentacular organs found on the 8th abdominal segment is now easily observed as well. The 3rd instar takes about 5 days to complete with the body length reaching about 9-10mm.

Two views of a 3rd instar caterpillar, length: 7.2mm.

Two views of a late 3rd instar caterpillar, dormant prior to its moult, length: 9mm.

Initially, the 4th instar mostly resembles the late 3rd instar caterpillar closely in coloration and most features. One obvious change is that the dorsal conicao protrusions from the 3rd thoracic segment to 3rd abdominal segment are now fused together to form a contiguous dark brown ridge. As growth progresses, the body color becomes uniformily purplish brown, and the anterior end becomes pointed with two tips closely spaced. The 4th instar takes about 3 days to complete with the body length reaching about 19-20mm. As it lays dormant prior to its moult, the body colour is mostly greyish brown.

Two views of a newly moulted 4th instar caterpillar, eating its exuvia.

Two views of a 4th instar caterpillar, later in this stage, length: 19mm.

Two views of a late 4th instar caterpillar, dormant prior to its moult.

The 5th instar caterpillar is initially reddish brown in body colour, but becoming darker as growth progresses. By day 4 of this instar, the body base colour is almost black to dark chocolate. At the same time, pale beige brown markings appear in mid-abdomen and posterior segments, and wavy markings flank the dorsum of the abdominal segments.

Two views of a newly moulted 5th instar caterpillar, eating its exuvia.

Two views of a 5th instar caterpillar, early in this stage, length: 18mm.

Two views of a 5th instar caterpillar, length: 27mm.

Two views of a 5th instar caterpillar, length: 29mm.

After about 6-7 days of feeding and reaching a length of about 32mm, the caterpillar stops food
intake, and its body gradually shortened and body base colour decolorised to a dull shade of
greyish green. The caterpillar would wander around in
seek of a pupation site which is typically a spot on a stem or branch. At this site, the pre-pupatory caterpillar prepares for
pupation by spinning a silk pad to which it
attaches itself via its anal claspers. After 1 day as a
pre-pupa, pupation takes place. The pupa has two prominent dorsal protuberances. It is predominantly pale to dark greyish brown with powdery green patches decorating its surface. There are also cryptic markings in orange, white and green to add to the concealment effect.
Pupal length: 18-20mm.

Two views of an immobile pre-pupa of the Great Imperial.

Two views of a pupa of the Great Imperial.

7-8 days later, the pupa turns rather dark, first in the wing pad and thorax,
then progressively in the abdomen. The next day, the pupal stage
comes to an end with the emergence of the adult
butterfly.

Two views of a mature pupa of the Great Imperial.

A newly eclosed Great Imperial waiting for its wings to expand fully near its pupal case.References:

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